Chapter 12 : Pathogenic Bacteria, Major Scourges, and New Diseases

Abstract:

Infectious diseases occur when a pathogenic agent (bacterium, virus, parasite, or fungus) succeeds in multiplying in an organism. Generally the agent is not present before the beginning of the illness, although members of the normal bacterial microbiota can cause opportunistic infections if the host's status suddenly changes, that is, if its natural immunity is impaired by immunosuppressive therapy, another infection, injury, or excessive fatigue or stress. However, most diseases are of human or, more often, animal origin. Zoonotic diseases, which are diseases transmitted from animals to humans, are most frequently transmitted by insects (such as fleas, flies, mosquitoes) or arthropods (such as ticks) that either carry the pathogen themselves or are vectors for infections in other animals (rats, various rodents, and domestic animals).